Rose, Angela M.C.Kissling, EstherGherasim, AlinCasado, ItziarBella, AntoninoLaunay, OdileLazăr, MihaelaMarbus, SierkKuliese, MonikaSyrjänen, RitvaMachado, AusendaKurečić Filipović, SanjaLarrauri, AmparoCastilla, JesúsAlfonsi, ValeriaGaltier, FlorenceIvanciuc, AlinaMeijer, AdamMickiene, AukseIkonen, NiinaGómez, VerónicaLovrić Makarić, ZvjezdanaMoren, AlainValenciano, MartaI-MOVE Hospital study team2021-04-052021-04-052020-05Influenza Other Respir Viruses. 2020 May;14(3):302-310. doi: 10.1111/irv.12714. Epub 2020 Feb 5.1750-2640http://hdl.handle.net/10400.18/7643Background: Influenza A(H3N2), A(H1N1)pdm09 and B viruses co-circulated in Europe in 2017-18, predominated by influenza B. WHO-recommended, trivalent vaccine components were lineage-mismatched for B. The I-MOVE hospital network measured 2017-18 seasonal influenza vaccine effectiveness (IVE) against influenza A(H3N2) and B among hospitalised patients (≥65 years) in Europe. Methods: Following the same generic protocol for test-negative design, hospital teams in nine countries swabbed patients ≥65 years with recent onset (≤7 days) severe acute respiratory infection (SARI), collecting information on demographics, vaccination status and underlying conditions. Cases were RT-PCR positive for influenza A(H3N2) or B; controls: negative for any influenza. "Vaccinated" patients had SARI onset >14 days after vaccination. We measured pooled IVE against influenza, adjusted for study site, age, sex, onset date and chronic conditions. Results: We included 3483 patients: 376 influenza A(H3N2) and 928 B cases, and 2028 controls. Most (>99%) vaccinated patients received the B lineage-mismatched trivalent vaccine. IVE against influenza A(H3N2) was 24% (95% CI: 2 to 40); 35% (95% CI: 6 to 55) in 65- to 79-year-olds and 14% (95% CI: -22 to 39) in ≥80-year-olds. Against influenza B, IVE was 30% (95% CI: 16 to 41); 37% (95% CI: 19 to 51) in 65- to 79-year-olds and 19% (95% CI: -7 to 38) in ≥80-year-olds. Conclusions: IVE against influenza B was similar to A(H3N2) in hospitalised older adults, despite trivalent vaccine and circulating B lineage mismatch, suggesting some cross-protection. IVE was lower in those ≥80 than 65-79 years. We reinforce the importance of influenza vaccination in older adults as, even with a poorly matched vaccine, it still protects one in three to four of this population from severe influenza.engAgedAged, 80 and overCase-Control StudiesCross ProtectionEuropeFemaleHospitalizationHumansInfluenza A Virus, H3N2 SubtypeInfluenza B virusInfluenza VaccinesInfluenza, HumanMaleRespiratory Tract InfectionsSeasonsVaccine PotencyDeterminantes da Saúde e da DoençaInfecções Respiratóriasjournal article10.1111/irv.12714